Consumers living in hot, humid climates, or consumers with oily skin, desire cosmetic products that have unique tactile properties during use. Specifically, such products should, upon application to the skin, deliver a high skin friction and a matte finish to overcome the oily skin feel and shiny skin appearance. The greater the increase in skin friction, the less greasy the user perceives the product to be. See Laufer et al., Objective Measurement and Self-Assessment of Skin-Care Treatments, Cosmetics and Toiletries Magazine, Vol. 111, June 1996, pp. 92–96.
More specifically, the typical sensory and optical features of these high skin friction and matte finish creams, also known as vanishing creams, are: 1) provide a dry, draggy, non-greasy feel to skin; 2) provide a non-shiny, matte finish; 3) spread easily on the skin; 4) absorb or “vanish” rapidly into the skin. The traditionally used vanishing creams contain high levels of stearic acid and alkaline metal soap as an emulsifier, which is important to physical stability of the product. The soap is formed by the in situ neutralization with caustic potash or other alkali on a portion of the stearic acid. Consequently, the creams made by saponification of stearic acid have a pH limit, i.e., greater than 5.7, in order to maintain the right balance of acid and acid soap. The anionic soap becomes inactive in acidic conditions in which hydrolysis occurs, resulting in undissociated stearic acid, and therefore causes physical stability problem at low pH.
The lack of physical stability of the acid soap emulsified vanishing creams at low pH is a disadvantage that restricts the use therein of valuable acidic benefit actives, such as alpha-hydroxy carboxylic acids, because the acidic actives reduce the pH of the compositions. However, emerging trends in skin care have required that vanishing cream formulations be adapted to incorporate acidic skin benefit agents. U.S. Pat. No. 6,153,177 (Bartolone et al.) discloses vanishing creams containing acid soap which have a pH above 5 and, therefore, include alkali or alkaline earth metal salts of alpha-hydroxy acid (AHA) to achieve skin lightening benefit. Care was taken not to include the acid form of AHA into the formulation in order to avoid destabilization of the base by the acid for the reasons stated above. However, it is generally accepted that actives in their acidic form penetrate the skin better than their ionized, and salt or electrolyte tends to affect the sensory feel of soap-based vanishing cream form. See Percutaneous Penetration Enhancers, CRC press, pp. 407 (1995). Therefore, it was clear that further work was necessary in order to enhance the performance of vanishing creams in delivery of acidic skin benefit agent, while maintaining the sensory attributes of traditional vanishing creams.
WO 01/70187 (Dwiwahyu et al.) disclose low pH (2–4.8), non-acid soap vanishing cream with enhanced skin benefit properties. A C8–C22 fatty acid substituted saccharide is used to stabilize the low pH stearic acid-based vanishing cream. Although these compositions are said to deliver an acidic skin benefit agent, the sensory characteristics of traditional vanishing creams have not been realized, which is believed to be due to the lack of a proper emulsifier system.
U.S. Pat. No. 4,536,519 (Suzuki, et al) discloses emulsified cosmetic compositions, including vanishing cream, using a neutralized phosphoric acid ester as an emulsifier, a nonionic surfactant with HLB<6 and fatty components including natural oil, wax, fat, and fatty acid or alcohol at pH of neutral to weakly acidic. These compositions, however, lack the sensory characteristics of traditional vanishing creams, and that is believed to be due to the lack of a proper emulsifier system.
Therefore, there is a need to provide a pH insensitive and stable cosmetic composition which not only maintains the unique sensory characteristics of vanishing cream but also enable to incorporate pH sensitive skin benefit agents.